1. Field of the Invention
The present invention relates to a multi-tone optical mask, a method of manufacturing the multi-tone optical mask and a method of manufacturing a thin-film transistor (TFT) substrate by using the multi-tone optical mask. More particularly, the present invention relates to a multi-tone optical mask capable of improving a manufacturing efficiency of a TFT substrate, a method of manufacturing the multi-tone optical mask and a method of manufacturing a TFT substrate by using the multi-tone optical mask.
2. Description of the Related Art
In general, a liquid crystal display (LCD) apparatus includes a flat display substrate. The display substrate includes a plurality of switching devices and a plurality of signal lines. The switching devices control a plurality of pixels, and the signal lines provide the switching devices with electrical signals.
The LCD apparatus includes a thin-film transistor (TFT) substrate having a plurality of TFTs, a color filter substrate having a color filter and a liquid crystal layer interposed between the TFT substrate and the color filter substrate. The LCD apparatus controls the liquid crystal layer by using signals applied to the TFTs to display an image.
The TFT substrate is manufactured through a plurality of layer-deposition processes and a plurality of photolithography processes. A manufacturing cost of the TFT substrate depends on the number of the photolithography processes.
In order to reduce the number of optical masks required for the photolithography processes, a photoresist pattern capable of etching a plurality of layers may be formed using one optical mask. Alternatively, a multi-step pattern having a plurality of steps may be formed by using one optical mask.
For the above, a method of exposing a positive photoresist layer to light by using a slit optical mask having a slit portion corresponding to a selected area of a substrate to form a photoresist pattern having a different thickness has been developed. Furthermore, a half-tone optical mask, of which a slit portion is substituted for a material having a proper light-transmittance to improve uniformity of a slit portion, has been developed.
However, when the slit optical mask is used, a residual photoresist layer corresponding to the slit portion is non-uniform. Furthermore, a photoresist pattern having a relatively great width may not be formed using the slit optical mask. The half-tone optical mask has three light-transmittances corresponding a transmitting area, a half-tone area and a non-transmitting area. Thus, a photoresist pattern formed using the half-tone optical mask may not have various thicknesses. Particularly, a line pattern formed under the photoresist pattern is non-uniform depending on disposition of the line pattern, disposition density of the line patterns, and the shape of the line pattern.